(1) Field of the Invention
The present invention relates to a transparent electroconductive coating film-forming paste which is useful for forming any desired shape of a transparent electroconductive coating film composed of a metal oxide on a substrate such as glass by screen printing and sintering, and a process for the preparation of this paste.
(2) Description of the Prior Art
It is known that a coating film of an oxide of Cd, In or Sn formed on a glass or ceramic substrate is transparent and has good electroconductivity. This coating film is used for semiconductor elements, liquid crystal display devices or as a freeze preventing electroconductive film on window glass. The application ranges of these coating films are recently broadened. Such metal oxide type transparent electroconductive coating films have formed by a chemical spray methods, vacuum deposition methods and screen printing methods.
The chemical spray method is advantageous when a coating film having a relatively large area is desired, but when a coating film having a fine and complicated shape is desired, an additional step such as a photo-etching step becomes necessary and the method is disadvantageous from the economical viewpoint. A mask vacuum deposition method has recently been developed which makes the photo-etching treatment unnecessary. However, since vacuum deposition of a large quantity of a metal oxide is impossible, this method is not suitable for mass production. The screen printing method is free from the foregoing disadvantages of chemical spray and vacuum deposition methods and is advantageous in that any desired shape of coating film can be formed by printing and sintering and the waste water treatment associated with the etching treatment need not be performed. However, the stability of transparent electroconductive coating film-forming pastes employed in the screen printing method is poor, the adaptability of the paste to the screen printing operation is bad, and the electroconductivity is not uniform in the formed coating films.